The present invention relates to wireless transmitters and receivers for transmitting and receiving digital data and, in particular, to transceiver systems that control transmitter parameters such as physical transmission bit rate, data byte-order, and retransmission attempts according to designated or imputed usefulness of the data.
Wireless transceivers, used in mobile devices such as cell phones and computers, transmit digital data impressed onto a physical signal such as a radio wave. The parameters of the physical transmission may include, for example, frequency of the radiowave, the modulation system (e.g., quadrature amplitude modulation), the encoding technique (e.g. Grey code), the signal strength, and the physical bit rate of the transmission. Typically, wireless transmitters will change some of the transmission parameters dynamically depending on the channel condition, for example, changing the physical bit rate, according to the amount of interference on the channel as indicated by dropped packets. Communication between the transmitter and receiver help establish these channel conditions.
Communication between a transmitter and receiver are also defined by higher-level protocols that handle problems of interference between transmitters (channel contention), the return of acknowledgment signals, and the retransmission of lost data. Examples of such protocols include, for example, the 802.11 family of wireless standards promulgated by the Institute of Electrical and Electronics Engineers hereby incorporated by reference.
Common wireless channels provide less bandwidth than physical conductors or optical media and for this reason, the transmission of high-bandwidth content such as high quality video can substantially tax common wireless networks. This problem is commonly addressed by compression of the video signal, for example, using the MPEG standards promulgated by ISO/IEC and hereby incorporated by reference. Such compression may process a block of data such as a Group of Pictures (GOP) comprising, for example, frames of a movie. Data reduction is obtained by using data of earlier or later frames to reconstruct other frames, for example, by sharing common portions of the frames that do not change. In this way, the amount of frame data that must be separately transmitted is reduced.
Network coding can be used to reduce the retransmission of data to multiple receivers by combining (coding) multiple data units of retransmitted data to be decoded by receivers using previously received data.
Even with current compression systems and network coding, transmitting high quality video to multiple receivers using wireless network standards can be difficult. Such transmissions to multiple users of the video stream would be desirable, for example, in an educational environment to permit students to follow remote lectures.